To determine the influence of sperm parameters inseminated on the outcome of intrauterine insemination (IUI) in patients undergoing ovarian stimulation with clomiphen citrat (CC) or human menopausal gonadotropin (HMG) therapy, a retrospective review was performed for 2 years on data from the IUI program. 190 couples underwent a total of 268 IUI cycles in which CC or HMG was used for ovulation induction. The initial sperm concentration (mil/ml), motility (percent), preprocessing total motile sperm (TMS) count (million), fast motile sperm (percent) and postprocessing sperm concentration (mil/ml), motility (percent), TMS count, fast motile sperm (percent), sperm morphology, hypoosmotic swelling (HOS) scores, semen leuocytes, and bacteria were analyzed. 268 inseminations were followed by a pregnancy rate of 12% and couple pregnancy rate of 17%. On multivariable logistic regression analysis, total motile sperm (TMS) count, percent motility, and percent of fast motile sperm were independent prognostic factors of fertility. The impact of the preprocessing and postprocessing sperm parameters on pregnancy outcome after IUI was evaluated. There was a trend toward an increasing percent of conception with increasing TMS count, motility, and percent of fast motile sperm. The TMS count, motility and percent of fast motile sperm independently predict success with IUI. Patients with original sperm motility > or = 30% had a higher cumulative pregnancy rate (74%) than patient with motility < 30% (p < 0.005). Pregnancy rate increased 4 times with motility of > or = 30%.